US7031561B2 - Monolithic integration of micro-optics circuits and RF circuits - Google Patents

Abstract

A chip for integrating functions performed by micro-optics and RF circuits including at least one optical function module that receives an optical signal and performs at least one of a plurality of optical functions. A RF function module that receives a RF signal and perform at least one of a plurality of RF functions. The at least one optical function module and the RF function module provides a monolithic integration of optics and RF circuits on the chip.

Description

PRIORITY INFORMATION

This application claims priority from provisional application Ser. No. 60/300,296 filed Jun. 22, 2001.

This invention was made with government support under Grant Number DMR-9808941 awarded by NSF. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

The invention relates to the field of communications, and in particular to the monolithic integration of planar lightwave circuits or integrated optics RF circuits.

There are currently several modes of communication that are in use. Wireless and optical communications are two of the newer forms of communication and have been pursued in separate fields. There have been several attempts to combine these two forms of communications at the chip level. One of these attempts is the use of fiber to the home (FTTH) optical communications, which provides enormous bandwidth, but has a large overhead. However, it is a fixed line and does not meet the necessary requirements for wireless applications. Another is the radio frequency (RF) approach, which can provide the convenience of wireless but it is bandwidth limited.

There is a need in the art to combine these two modes of communications so that RF monolithic microwave circuits (MMICs) and discrete optics components can be integrated to form a bridge between RF and fiber optic communication technologies.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a chip for integrating functions performed by micro-optics and RF circuits. The chip includes one or more optical function modules for assembling a plurality of optical functions. The one or more optical function modules receive an optical signal, and perform at least one of the plurality of optical functions. A RF function module assembles a plurality of RF functions. The RF function module receives a RF signal, and performs at least one of the plurality of RF functions. The one or more optical function modules and the RF function module provide a monolithic integration of optics and RF circuits on the chip.

According to another aspect of the invention, there is provided a hybrid circuit including micro-optics and RF circuits. The hybrid circuit includes at least one optical function module that receives or transmits an optical signal and performs at least one of a plurality of optical functions. A RF function module that receives a RF signal and perform at least one of a plurality of RF functions. The at least one optical function module and the RF function module are integrated on a single microchip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a planar chip for implementing the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of aplanar chip2 for implementing the invention. The planar chip includes a first externaloptical fiber4. The first externaloptical fiber4 receives an optical signal, and provides the optical signal to theplanar chip2 as input. Given the structural arrangement of optical fibers, the first externaloptical waveguide4 has a mode size of approximately 8–10 μm. The mode size can vary depending on the specific carrier properties of the optical signal used in the optical fiber. The first externaloptical fiber4 connects theplanar chip2 to optical signals received externally. In other embodiments, there can be more than one input optical fiber to theplanar chip2. Also, the one or more optical fibers can act as output fibers or simultaneously act as both input and output fibers in other embodiments.

The optical signals that are received by the first externaloptical fiber4 are provided to a first waveguide mode converter module6, within theplanar chip2. The first waveguide mode converter module6 is designed monolithically on thechip2, and converts the mode size of the optical signal to less than 3 μm. Also, the first waveguide mode converter module6 is connected to one or morehigh index waveguides30. Thehigh index waveguides30 provide a channel for propagating the optical signals to thevarious modules6,8, and10 within the interior of theplanar chip2 without incorporating any substantial lost to the optical signal.

The more waveguide structures that are used in the highindex difference waveguides30, the higher the density of optical functions, because the optical functions and their associated optical routing scale inversely in size with respect to index contrast. However, care must be taken to ensure that loss is kept at a minimum. Thehigh index waveguides30 can include waveguide structures that are made from different high index materials, and the indexes can vary for each waveguide structure. Also, thehigh index waveguides30 interconnect the first waveguide mode converter module6 to a first optical function module8.

The first optical function module8 receives an optical signal from a first set of thehigh index waveguides30 as input, and also receives a control electronic signal from acontrol module32 as input. The first optical function module8 is an integration of more than one optical function connected with one or more optical waveguides. This includes, but is not limited to, optical components, such as filters, splitters, dispersion compensation components, resonators, fiber couplers, switches, polarization rotators, frequency mux/demux, or the like. The electronic signal input is used to actuate the optical functions to be performed by the first optical function module8. In other embodiments, thefirst function module30 can perform various optical functions simultaneously without incurring substantial loss to the performance of theplanar chip2. After performing its optical functions, thefirst function module30 provides its output to a second set of thehigh index waveguides30.

The second set of thehigh index waveguides30 propagates this output to a first optical-RF transducer10. The optical-RF transducer10 receives the output optical signal from the first optical function module8, and proceeds to convert the optical signal into a RF signal. The RF signal has substantially the same properties as its optical counterpart, except that the frequency of the optical signal is in the RF range, and will have the same characteristics of microwave signals. Also, the RF signal is decoupled from its optical counterpart, but includes the optical function properties performed on its optical signal counterpart by the first optical function module8.

The optical-RF transducer10 outputs the RF signal to afirst RF waveguide36. TheRF waveguide36 propagates the RF signal to aRF function module12, and is designed specifically to incorporate minimal loss to the RF signal. The dimensions of theRF waveguide12 can vary depending on the distance between the optical-RF transducer10 and theRF function module12, and the area of theplanar chip2.

TheRF function module12 receives as input the optical signal propagated by theRF waveguide36, and an electronic control signal from thecontrol module32 to actuate theRF function module12. Also, theRF function module12 is an integration of more than one RF f unction connected with one or more RF waveguides. This includes, but is not limited to, RF components, such as filters, splitters, dispersion components, resonators, fiber couplers, switches, RF amplifiers, transistors, antennae, and frequency mux/demux. Examples of RF functions that are performed by theRF function module12 include but are not limited to detectors, lasers, modulators, WDM mux/demux, attenuators, and gain elements.

Alternatively, a RF signal can be coupled onto theplanar chip2 usingRF waveguides40 and42. This allows theplanar chip2 to receive both RF and optical signals. The dimensions of theRF waveguides40 and42 are dependent on the distance between theRF function module12 andinput ports22 and24, and the area of theplanar chip2. The larger the distance between theinput ports22 and24, the higher the risk of having substantial loss in an input RF signal. Therefore, theRF waveguides40 and42 are formed with materials, which minimize loss over long distances, and each of theRF waveguides40 and42 can be different from one another. In other embodiments, the distance between theRF function module12 andinput ports22 and24 can vary, thus requiring different types of waveguides to be used to minimize loss.

Also, theRF waveguides40 and42 can be used as output channels for RF signals, which are processed by theRF function module12. In this embodiment, theports22 and24 become output ports. The invention can allow theplanar chip2 to receive both optical signals and RF signals simultaneously for processing, where theports22 and24 can be both input and output ports simultaneously also.

When a RF signal is provided as input toports22 or24, theRF function module12 performs its RF functions, and provides its output to aRF waveguide38. TheRF waveguide38 is similar to theRF waveguide36, and propagates the output RF signal of theRF function module12 to a RF-optical transducer14. Also, theRF waveguide38 is designed specifically to minimize loss to the output RF signal. The dimensions of theRF waveguide38 can vary depending on the distance between the RF-optical transducer14 andRF function module12, and the area of theplanar chip2.

The RF-optical transducer14 receives the output optical signal from theRF function module12, and proceeds to convert the signal into an optical signal. The optical signal has substantially the same signal properties as its RF counterpart, except that the frequency of the RF signal is in the optical range. The optical signal is decoupled from its RF signal counterpart, but includes RF function properties performed on its RF signal counterpart by the RF function module8. The RF-optical transducer14 provides its output tohigh index waveguides34.

Thehigh index waveguides34 are similar to thehigh index waveguides30, and they provide a channel for propagating optical signals tomodules16 and18 within the interior of theplanar chip2 without incorporating any substantial lost to the optical signal. As similarly described for thehigh index waveguides30, the more waveguide structures that are used in the highindex difference waveguides34, the higher the density of optical functions, because loss is kept at a minimum. Thehigh index waveguides34 can also include waveguide structures that are made from different high index materials, and the indexes can vary for each waveguide structure. Thehigh index waveguides34 interconnect the RF-optical transducer14 to a secondoptical function module16.

The secondoptical function module16 receives an optical signal associated with the output of the secondoptical function module14 from a first set of thehigh index waveguides34 as input, and also receives a control electronic signal from acontrol module32 as input. The secondoptical function module16 is an integration of more than one optical function connected with one or more optical waveguides, such as filters, splitters, dispersion compensation components, resonators, fiber couplers, switches, polarization rotators, frequency mux/demux, or the like. Examples of optical functions that are performed by the secondoptical function module16 include but are not limited to detectors, lasers, modulators, WDM, mux/demux, attenuators, and gain elements. The electronic signal input is used to actuate the optical functions to be performed by the secondoptical function module16.

In other embodiments, the secondoptical function module16 can perform various optical functions simultaneously without incurring substantial loss to the performance of theplanar chip2, and provides its output to a second set of thehigh index waveguides34.

A second waveguidemode converter module18 receives as input from the second set of thehigh index waveguides34 the output from the secondoptical function module16, and proceeds to convert the mode of its input optical signal. In particular, the second waveguidemode converter module18 converts a mode of an optical signal to be useable in a fiber optic line. In this case, an optical signal is converted from a mode that is less than 2 μm to a mode that is greater than 3 μm. Most fiber optic lines require modes between 8 and 10 μm. Therefore, the secondwaveguide mode converter18 converts the mode of an optical signal within the range that is used in conventional fiber optic lines.

The secondwaveguide mode converter18 provides its output to a second external outputoptical fiber20. The second externaloptical fiber20 receives the converted optical signal. Given the structural requirements of an optical fiber, the second external outputoptical fiber20 has a mode size of approximately 8–10 μm. The mode size can vary depending on the specific carrier properties of an optical fiber. The second external outputoptical fiber20 outputs optical signals associated with RF processing. There can be more than one output optical fiber to theplanar chip2.

Theoptical fibers4 and20 can be used as either input or output fibers simultaneously. In this embodiment, theoptical fibers4 and20 have diameters of approximately 10 μm, however, this can vary. Also, optical fibers with mode sizes ranging from 4–50 μm can also be used in accordance with the invention.

Thecontrol module32 receives as input from aninput port26 external control signals from a controller to manage themodules8,12, and16. Also, thecontrol module32 processes the signals from the controller into a format useable by the modules,8,12, and16, and outputs interior control signals tomodules8,12, and16. These interior control signals include information regarding which type of functions thesemodules8,12, and16 will perform, and selective data to be provided by the modules812, and16 to the controller. When thecontrol module32 receives this data, it immediately processes the information into a format useable by the controller and outputs this information throughoutput port28 to the controller. Also, thecontrol module32 can be used to monitor the workload of themodules8,12, and16, therefore improving the throughput of information going in and out of theplanar chip2. Thecontrol module32 uses aline44 to receive and output information to theoptical module8,12, and16, respectively.

The invention allows theoptical module8 and16 andRF module12 to communicate in a unidirectional or bi-directional fashion without limiting the performance of thesystem2. For example,optical module16 can provide its output to themode converter module18 andRF module12 using theline44. The same occurs formodules8 and12, respectively. Theline44 interconnects theoptical modules8 and16 andRF module12 to each other, and allows unidirectional and bi-directional communication to occur between themodules8,12, and16, respectively.

Theplanar chip2 uses silicon mixed technology integrated with a CMOS compatible high index waveguide. In this technology, RF mixed signal (digital and analog) integrated circuits are made using standard silicon CMOS processes on a silicon substrate. Detectors can also be integrated with these components. Depending on the wavelength, silicon, germanium, or germanium detectors can be used in accordance with the invention. Integrated optic wavelength technology using one or a combination of silicon CMOS compatible materials can also be fabricated on this substrate.

A designer of such monolithically integrated optical and RF mixed signal circuit has several options in a choosing a wafer substrate, a wavelength of operation, waveguide and detector materials, and waveguide forming techniques. The choice of the substrate is determined largely by cost vs. performance trade-offs. The RF devices made on compound semiconductor materials can operate at much higher frequencies, while devices made on silicon have as a general rule much lower cost. Using silicon also has the added advantage of being able to leverage off existing silicon foundries. The choice of wavelength depends on the wavelength of the optical carrier. This wavelength determines the material choice for the waveguide and the detector. The choice between growth, deposition, or wafer bonding to form a waveguide layer is based on a cost vs. performance tradeoff. Wafer bonding usually allows greater flexibility in design, since compound semiconductor wafers can be bonded to silicon wafers, whereas growth is cheaper.

The invention can be used with in RADAR or electronic warfare applications. Full-systems or even sub-systems on a chip can be achieved with such technology. Also, the invention can be used in fiber optics communication systems as well as in high speed computing applications. This technology can be made relatively cheap and will provide the user with an enormous amount of bandwidth coupled with the convenience of wireless RF. RF and optical transducers and processors will seamlessly mate the RF and optics technologies together. The invention further provides low loss, low cross talk, and low EMI susceptibility. Also, electronic CMOS integrated circuits can be added for more functionality without substantially burdening the designer.

Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.

Claims (32)

1. A hybrid circuit including micro-optics and RF circuits, said hybrid circuit comprising:

at least one optical function module that receives or transmits an optical signal and performs at least one of a plurality of optical functions; and

a RF function module that is coupled to said at least one optical function module and receives or transmits a RF signal and performs at least one of a plurality of RF functions,

wherein said at least one optical function module and said RF function module are integrated on a single microchip so as to permit optical and RF computations to be performed on either said optical signal or said RF signal,

wherein at least one RF waveguide provides directly to said RF function module at least one RF signal as input.

2. The hybrid circuit ofclaim 1 further comprising at least one external input optical fiber inputting said optical signal to said microchip.

3. The hybrid circuit ofclaim 2 further comprising at least one external output optical fiber outputting optical signals from said microchip.

4. The hybrid circuit ofclaim 2 further comprising a first waveguide mode converter coupled to said at least one external input optical fiber for receiving said optical signal from said at least one external input optical fiber and converting the mode of said optical signal.

5. The hybrid circuit ofclaim 4, wherein said first waveguide mode converter converts said mode size of said optical signal to less than 3 μm.

6. The hybrid circuit ofclaim 4 further comprising a first set of high index optical waveguides interconnecting said first waveguide mode converter and at least one of said at least one optical function module.

7. The hybrid circuit ofclaim 6 further comprising one or more optical-RF transducers for converting output optical signals from said at least one optical function modules into RF signals.

8. The hybrid circuit ofclaim 7 further comprising at least one RF waveguide interconnecting said one or more optical-RF transducers and said RF function module.

9. The hybrid circuit ofclaim 6 further comprising a second set of said high index optical waveguides interconnecting said RF function module and at least one of said optical function modules.

10. The hybrid circuit ofclaim 1 further comprising one or more RF-optical transducers for converting output RF signals of said RF function module into optical signals.

11. The hybrid circuit ofclaim 10 further comprising at least one RF waveguide for interconnecting the RF function module and said one or more RF-optical transducers.

12. The hybrid circuit ofclaim 1 further comprising a control module for providing control signals to said at least one optical function module and said RF function module.

13. The hybrid circuit ofclaim 12, wherein said control module requests data from said at least one optical module and RF function module for an external controller.

14. The hybrid circuit ofclaim 13, wherein said control module receives external control signals from said external controller, said control module processing said external control signals in a format useable by said one or more optical function modules or said RF function module.

15. The hybrid circuit ofclaim 14, wherein said control module receives data from said at least one optical function module or said RF function module to be provided to said external controller, said control module processing said data in a format useable by said external controller.

16. The hybrid circuit ofclaim 1, wherein said at least optical function module and said RF function module exchange information unidirectional or bi-directional fashion between said modules.

17. A chip for integrating functions performed by micro-optics and RF circuits, said chip comprising:

at least one optical function module that receives an optical signal and performs at least one of a plurality of optical functions; and

a RF function module that is coupled to said at least one optical function module and receives a RF signal and perform at least one of a plurality of RF functions,

wherein said at least one optical function module and said RF function module provides a monolithic integration of optics and RF circuits on said chip so as to permit optical and RF computations to be performed on either said optical signal or said RF signal; and

wherein at least one RF waveguide provides directly to said RF function module at least one RF signal as input.

18. The chip ofclaim 17 further comprising at least one external input optical fiber inputting said optical signal to said chip.

19. The chip ofclaim 18 further comprising at least one external output optical fiber outputting optical signals from said chip.

20. The chip ofclaim 18 further comprising a first waveguide mode converter coupled to said at least one external input optical fiber for receiving said optical signal from said at least one external input optical fiber and converting the mode of said optical signal.

21. The chip ofclaim 20, wherein said first waveguide mode converter converts said mode size of said optical signal to less than 3 μm.

22. The chip ofclaim 20 further comprising a first set of high index optical waveguides interconnecting said first waveguide mode converter and at least one of said at least one optical function module.

23. The chip ofclaim 22 further comprising one or more optical-RF transducers for converting output optical signals from said at least one optical function modules into RF signals.

24. The chip ofclaim 23 further comprising at least one RF waveguide interconnecting said one or more optical-RF transducers and said RF function module.

25. The chip ofclaim 22 further comprising a second set of said high index optical waveguides interconnecting said RF function module and at least one of said optical function modules.

26. The chip ofclaim 17 further comprising one or more RF-optical transducers for converting output RF signals of said RF function module into optical signals.

27. The chip ofclaim 26 further comprising at least one RF waveguide for interconnecting the RF function module and said one or more RF-optical transducers.

28. The chip ofclaim 17 further comprising a control module for providing control signals to said at least one optical function module and said RF function module.

29. The chip ofclaim 28, wherein said control module requests data from said at least one optical module and RF function module for an external controller.

30. The chip ofclaim 29, wherein said control module receives external control signals from said external controller, said control module processing said external control signals in a format useable by said one or more optical function modules or said RF function module.

31. The chip ofclaim 30, wherein said control module receives data from said at least one optical function module or said RF function module to be provided to said external controller, said control module processing said data in a format useable by said external controller.

32. The chip ofclaim 17, wherein said at least optical function module and said RF function module exchange information in a unidirectional or bi-directional fashion between said modules.

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